You should look at the American Stampless Cover Catalog for listings of markings for the pre 1855 period. The books are currently being updated (slowly), but you can find info on them and the preliminary listings for the various states at the U.S. Philatelic Classics Society website - uspcs.org
Direct link to the pages with the draft sections is:
http://www.uspcs.org/resource-cente.../your-input/Also, you can look on Jim Forte's site - postalhistory.com for what he might have in stock for Knoxville.
Jerry Palazzo, a dealer, is also the editor of the Tennessee Postal History Journal (or some such name). He authored an article in the last year for the USPCS Chronicle on Tennessee Post Offices Reopened During Federal Occupation
Hope that helps.